Professional meteorological observations follow standards set by the World Meteorological Organization. These standards specify instrument types, siting requirements, measurement intervals, and data quality criteria. While hobby stations rarely meet every requirement, understanding the principles helps you site your instruments better, interpret your data more accurately, and contribute meaningful readings to citizen observation networks. The WMO Instruments and Observations programme provides the authoritative reference for these standards. This guide translates the most relevant aspects into practical advice for station operators, connecting to the data validation practices in Publishing Fundamentals.

Instrument Siting Guidelines

Temperature and Humidity

WMO standard: sensors should be housed in a ventilated screen (Stevenson screen or equivalent) at 1.25–2.0 metres above ground, over a grass surface, away from buildings, trees, and paved surfaces. The intent is to measure the free air temperature without contamination from heat sources, shadows, or reflected radiation.

Practical compromise: most hobby stations cannot achieve ideal siting. Mount the sensor as far from buildings as practical, at least 1.5 metres above ground, in a location that does not receive direct afternoon sun reflection from walls or windows. A north-facing wall mount (in the Northern Hemisphere) is acceptable if the sensor is in a radiation shield and at least 1 metre from the wall surface.

Wind

WMO standard: anemometer at 10 metres above open, flat terrain with no obstructions within 10 times the height of the obstruction. This is rarely achievable in residential settings.

Practical compromise: mount the anemometer at the highest accessible point — typically the roof ridge. Accept that buildings and trees will affect readings. Wind speeds at lower heights are systematically lower than the 10-metre standard, and direction may be channelled by nearby structures. Noting your site limitations honestly is more valuable than ignoring them.

Rainfall

WMO standard: rain gauge at ground level in an open area, with no obstructions above 30° from the gauge rim. Nearby wind shields (turf walls or fence-panel arrays) reduce wind-induced under-catch.

Practical compromise: place the gauge away from overhangs and at least twice the height of nearby objects from those objects. Rooftop mounting introduces wind effects that cause under-reading of 10–20% in moderate wind. Ground-level in a sheltered garden corner is usually a better option than the roof.

Measurement Intervals

WMO synoptic observations are taken every 3 hours (00, 03, 06, 09, 12, 15, 18, 21 UTC) for standard reporting. Automated stations report more frequently — typically every 1 to 10 minutes.

For hobby stations publishing to the web, a 5-minute interval provides a good balance between temporal resolution and resource usage. Wind gusts should be sampled at the highest rate your station supports (often 2.5–3 seconds) and reported as the maximum in each publishing interval. Rainfall is accumulated continuously and reported as a running total.

Data Quality for Networks

If you contribute data to CWOP, Weather Underground, or similar networks, your data undergoes automated quality checks. Common rejection criteria include:

• Pressure readings more than 20 hPa from the nearest airport METAR
• Temperature readings more than 10°C from neighbouring stations under similar conditions
• Humidity fixed at exactly 0% or 100% for extended periods
• Wind speed or direction readings that never change (stuck sensor)

See Station Data Sanity Checks for practical validation techniques.

Troubleshooting Matrix

FAQ